Final answer:
Impurities generally lower the melting point of a substance by disrupting the lattice structure and making it easier for particles to transition from solid to liquid state.
Step-by-step explanation:
The effect of impurities on the melting point can vary depending on the nature of the impurities. In general, impurities tend to lower the melting point of a substance. This is because the presence of impurities disrupts the regular lattice structure of the substance, making it easier for the particles to overcome the intermolecular forces and transition from solid to liquid state.
For example, if you have a pure substance with a high melting point, adding impurities to it will likely lower the melting point. This can be seen in the production of aluminum, where the addition of impurities to cryolite reduces the melting point of the mixture and enables the extraction of aluminum at lower temperatures.
In some cases, impurities may have no effect on the melting point or even increase the melting point range. However, these cases are less common compared to impurities lowering the melting point.